Broadband tuning transformer permitting independent matching at adjacent frequencies



G. F. ENGEN RANSFORMER PERMITTING INDEPENDE Jan. 19, 1965 BROADBAND TUNING T MATCHING AT ADJACENT FREQUENCIES 3 Sheets-Sheet 1 Filed June 4. 1962 Jan. 19, 1965 G. F. ENGEN 3,166,725

BROADBAND TUNING TRANSFORMER PERMITTING INDEPENDENT MATCHING AT ADJACENT FREQUENCIES Filed June 4, 1962 3 Sheets-Sheet 2 TUA/ED Fae TUA/ED FOI? INVENTOR Gle/m F Engen ATTORNEY Jan. 19, 1965 G. F. ENGEN BROADBAND TUNING TRANSFORMER PERMITTING INDEPEND Filed June 4. 1962 3,166,725 ENT MATCHING AT ADJACENT FREQUENCIES 5 Sheets-Sheet 3 l llHl Rigi/5 /W INVENTOR V26 N,4L Glenn F frye/7 @S/LJ @Mw ATTORNEY United .States Patent O M This invention relates in general to a broad band tuning device for use in high frequency, electrical transmission systems and in particular to a broadband tuning transformer.

In the electrical communications field, extensive use is made of transmission lines such as waveguides and coaxial cables to transfer high frequency energy from a source to a power absorbing load. In most applications it is desirable to match the impedances of the load and source to the transmission line in order to achieve a maximum transfer of power, low standing-wave ratio, etc. To obtain these results, extensive use is made in the prior art of such tuning transformers as the multi-stub tuner, slide screw tuner, double-stub tuner. These'tuners,

however, provide an impedance match at only a single frequency, and the extent to which the impedance is matched at neighboring frequencies is often determined by chance or other factors over which, for practical purposes, one has little or no control.

It is therefore an object of the present invention to provide a tuning device for a transmission line which' permits an impedance match to be achieved at two or `more frequencies simultaneously.

This is accomplished by first using a conventional rtuner, which may be one of the types mentioned earlier, to obtain an impedance match at one of the frequencies, f1,

of interest. The second tuner, described just below, is then used to adjust for an impedance match at frequency f2, while retaining the existing impedance match at f1. Ifthe difference between f1 and f2 is small, the departure from an impedance match over the interval between the frequencies is usually quite small.

The problem of impedance matchinga waveguide, for example, may be visualized as one of introducing a reiiection of the proper magnitude and phase to balance out the existing reflection. In the conventional slide screw tuner, this is achieved by means of an adjustable probe. The depth to which the probe projects into the waveguide determines the amplitude of the reflection, while its phase is dependent upon the probes longitudinal position along the waveguide axis. In contrast, the second tuner of this invention provides an obstacle which can be made reflectionless at f1 while producing a reflection of selected amplitu-de and phrase at f2. Decoupling is provided by the tuner so that the adjustments making the obstacle reectionless at f1 are substantially independent of those producing the reflection at f2.

In the figures: Y

FIG. l is a first embodiment;

FIG. 2 is a pictorial of tuners 25 and 31 which are used in FIGS. l and 6;

FIG. 3 is a partial rear view of FIG. 2;

FIG. 4 is a section of FIG. 2 taken along line 4 4;

FIG. 5 is a section of FIG. 2 taken yalong line 5-5; and

FIG. 6 is a second embodiment of the present invention.

Referring to FIG. 1, the output of signal generator 10 is fed through waveguide 11 to load 12, whose impedance is to be matched to that of the waveguide at frequencies f1 and f2. The waveguide comprises sections 13 and 14, coupled together by 17. Section 14 is l 3,166,725 Patented Jan. 19, 1965 ICC coupled to the load by 19 and section 13 to generator 10 by member 20. Directional coupler 22 samples the reflected wave in waveguide 11 and, in conjunction with detector 23 and oscilloscope 24, permits the recognition of the required impedance match at f1 and f2. Tuner 25 is a conventional five-stub Ituner which includes stubs 26 and has the ability to match load 12 to the waveguide impedance at f1. It is understood that instead of this tuner other conventional types of waveguide tuners may be used.

In the adjustments described below, signal generator 10 applies either frequency f1 or f2, as required, to waveguide 11. The reflection at either frequency is determined by means of directional coupler 22, detector 23, and oscilloscope 24. f

Tuner 31 comprises probes 32 and 33, whose respective penetrations can be adjusted independently. In addition, as described below in connection with FIG. 2, an arrangement is provided for adjusting the spacing-between the probes and for transporting the probes simultaneously along the longitudinal axis of waveguide 11.

`Thus, proble 32 may be displaced relative to probe 33 inA direction D1 or D2 and the pair of probes may be vsimultaneously displaced along the waveguides axis in either direction D3 or D4.

For an arbitrary insertion of probe 33, its reflection at frequency f1 can be cancelled by inserting probe 32 a certain distance 'into' waveguide 11 and by adjusting the spacing between probes 32 and 33. In general, this Awould occur for approximately equal insertions of the probes and for a separation which is an odd multiple of `a quarter of a wavelength of waveguide 11, i.e., 11k/4.

Although the 'pair of probes is thus made reectionless at frequency f1, they will produce a reflection at frequency f2, whose amplitude is dependent upon the combined penetrations of probes 32 and 33 whose phase can be adjusted by moving them simultaneously along the axis of waveguide 11.

Referring to FIGS. 2 to 4, shaft 36, is positioned between supporting members 37, 38.l Angle-shaped members 41, 42 are attached to plates 43, 44, by suitable means, to provide probe carriages 45, 46. The carriages are slidably mounted on shaft 36 and slidably mounted on shaft 47 (FIG. 3) by ball bearings 48. The latter are mounted on plates 43, 44 by means of eccentric shafts 49.

' that when the knob is rotated clockwise, carriages 45,

46, and thus probes 32, 33, are moved simultaneously, as a uni-t, to the right; and when the knob is rotated counterclockwise, the probes move, as a unit, to` the left, as viewed in FIG. 2. When the carriages are clamped in position by the arrangement described immediately below, control disc 59 functions as a vernier for knob S6.

Control disc 60 is positioned on shaft 61. The shaft has left-hand threads on one end, which match the internal threads of member 41, and right-hand threads on the other end, which match the internal threads of member 42. Locking collar 62, controlled by bolt 65, is slidably mounted on shaft 36.

When threaded rod 64 is fastened to member 42 and bolt 65 is tightened, carriages 45, 46 are clamped in position. Control disc 6i) may then be rotated in one direction to move carriage towards carriage 46, or the disc may be rotated in the opposite direction to move carriage 45 away from carriage 46. Thus, rotation oi' disc 6d produces a displacement of probe 32 relative to probe 33, while rotation of knob 56 or disc 59 transports both probes simultaneously along the axis of waveguide section 14.

In a typical operation of the embodiment in FIG. l, stub-tuner 25 is adjusted for the proper insertion of probes 26 as required to obtain an impedance match at frequency f1. This operation is performed with both probes 32, 33 completely withdrawn, so that their eifect on the operation is negligible. Probe 33 is then inserted an arbitrary amount. The reflection of probe 33 at f1 is now eliminated by adjusting the penetration of probe 32 and its position relative to probe 33. The pair of probes 32, 33 is then moved back and forth longitudinally along the axis of waveguide section 14, and the effect upon the impedance match at frequency f2 is noted on oscilloscope 24. Because this pair of probes was previously adjusted to be reflectionless at frequency f1, this operation will not affect the impedance at f1. The penetrations of probes 32 and 33 are then progressively increased, maintaining at all `times their relative insertions and mutual spacing so that the tuner is reectionless at frequency f1, until a reflection ,at frequency f2 is produced having a magnitude suiciently great to cancel the existing reflection at frequency f3.

The procedure followed to obtain the later result comprises the following steps:

(l) The insertion of probe 33 is increased in arbitrary amounts;

(2) The insertion of probe 32 is increased and its position relative to probe 33 adjusted to maintain tuner 31 rellectionless at frequency f1.

These steps are repeated until the reliection provided f by tuner 31 has the magnitude required to cancel the existing reflection at frequency f2.

The pair of probes is then moved longitudinally along the axis of waveguide section 14 until its reection has the, proper phase to cancel the existing reflection a-t frequency f2.

It is noted that two types of longitudinal motions are permitted by tuner 31. One is the motion of probes 32, 33 simultaneously along the longitudinal axis of Waveguide section 14, and -the other is the motion of probe 32 with respect to probe 33.

It is also noted that four degrees of freedom are associated with probes 32 and 33. Two are used to maintain the existing impedance match at frequency f1, and two to obtain an impedance match at frequency f2. More specifically, the freedoms .associated with obtaining an impedance match at f2 are: the penetration of probe 33 and its longitudinal position with respect to waveguide 11; and the freedoms associated with continually maintaining the impedance match at f1 are: the insertion of probe 32 and its spacing relative to probe 33.

An essential feature of the present invention lies in the fact that the associated theory yields a straightforward sequence of adjustments by which a simultaneous impedance match at two or more frequencies may be obtained. To each value of insertion of probe 33, for example, there exists a unique value of adjustment of probe 32, which is readily recognized by means of the associated instrumentation. lt is this which distinguishes the present invention from the conventional five-stub tuner, for example. Although the latter device would also, in theory, permit one to achieve a simultaneous impedance match at two frequencies, the associated theory does not yield the features outline above. As a result, the adjustment procedure becomes a little more than a trail and error process which, because of the number of lindependent adjustments involved, is too difficult to be of practical value.

To obtain an impedance match at frequencies f1, jg, and f3 simultaneously, one may employ the embodiment in FIG. 6, wherein: the output of signal generator is applied through waveguide '76 to load 79. \Vaveguide 76 comprises sections and 8l. Section 80 is coupled to signal generator 75 by coupling member 84, and section 81 to load 79 by member 85. Tuner 25, which includes stubs 26 (FlG. 5), is a conventional live-stub tuner. Detector 92 is coupled to waveguide section S0 by means of directional coupler 93, and oscilloscope 94 is tied to the output of the detector.

Tuner 95 comprises elements 96 and 97. Element 96 includes probes 98, 99 and is similar to tuner 31, so that probe 98 may be displaced relative to probe 99 in either direction D5 or D6. In addition, there is an arrangement, like that shown in FIGS. 2 and 3, for displacing element 96 longitudinally in either direction D7 or D8, with respect to element 97, and for moving both 96 and 97 simultaneously in either direction D9 or D10 along the longitudinal axis of waveguide section S1. Element 97, which includes probes 109, lill, also resembles tuner 31. Hence, probe may be transported relative to probe 101 in either direction D11 or D12.

In the various operations described below, signal generator '75 applies either frequency f1, f2, or f3, as required, to waveguide 76. The reflection established in the waveguide is coupled through directional coupler 93 to detector 92, so that the waveform of the retiection is observed on oscilloscope 94.

In a typical operation of the embodiment disclosed in FIG. 6, it is desired to obtain an impedance match at frequency f3 while retaining lan existing match at frequencies fl and f2. Using tuners 25 and 31 and the procedure described above in connection with FlG. l, load 79 is matched to waveguide 75 at frequencies f1 and f2. The adjustment of tuner 95 to achieve the impedance match at f3, while retaining that at f1 and f2, proceeds as follows: probe 101 is inserted an arbitrary distance into waveguide section 81. Probe 10i) is adjusted in penetration and distance from probe 101 as required to make this pair of probes (element 97) rellectionless at f1. By use of element 96, as described earlier in conjunction with tuner 31 in FIG. l, the existing reilection from element 97 at f2 is now eliminated, while retaining the impedance match at f1. At this point, there will be no net reflection from the series of probes 93 to 101 at either of the frequencies f1 or f2, but there will, in general, be a reiiection at f3. The effect of this reflection upon the original reflection at f3 is then observed by moving probes 98 to 101 simultaneously along the axis of waveguide 76 in directions D9 or D10. lf a smaller or greater reiiection at f3 from probes 98 to 101 is required to cancel the original reection at f3, probe 101 is readjusted and the sequence of operations outlined above is repeated.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. If, for example, it is desired to match the impedance of waveguide 76 simultaneously at four frequencies, another tuner having eight probes, and similar in construction to tuner 95, would be inserted in the waveguide. ln general, each time the number of frequencies, Whose impedances are to be matched simultaneously, is increased by one, another tuner having twice the number of tuning elements as the preceding tuner must be added to the waveguide system.

What is claimed is:

l. ln a tuning device for a transmission line having a slot positioned along its longitudinal axis, a rst and second slidably mounted carriage, means for moving said rst carriage relative to said second carriage, means for moving said first and second carriage simultaneously as a unit along the longitudinal axis of said transmission line, a third, fourth, fifth and sixth carriage, a plurality of probes, each positioned on a respective one of the carriages, each probe extending through said slot into said transmission line, means for moving saidl fourth carriage relative to said third carriage and said fifth lcarriage relative to said sixth carriage, and means for moving said third, fourth, fifth and sixth carriage simultaneously as a unit along the longitudinal axis of said transmission line.

2. The device set forth in claim l including means positioned in said transmission line for providing an impedance match at a selected frequency. Y

3. In a tuning device for a transmission `line having a slot positioned along its longitudinal axis, a first and second slidably mounted carriage, a first and secondl adjustable probe positioned on the first and second carriage, respectively, each probeextending through said slot into said transmission line, first means for moving said first carriage relative to the second carriage, second means for moving said first and second carriage simultaneously as a unit along the longitudinal axis of said transmission line, and means positioned in said transmission line for providing an impedance match at a selected frequency.

4. In an arrangement for tuning a waveguide, said waveguide being dimensioned to support only one mode of popagation over a frequency range including -a first and second frequency, means for generating said first and second frequency, means for launching said first and second frequency in said mode in the waveguide, rst adjustsecond tuningmean-s comprises: means for maintainingr said second tuning means reiiectionless at said first frequency, and means for providing a reflection at the second frequency having an amplitude'and phase such that an impedance matchis provided at the last-mentioned frequency.

References Cited by the Examiner UNITED STATES PATENTS 6/54 King 333-73 OTHER REFERENCES Very High-Frequency Techniques, vol. 1, Radio Research Laboratory, New York, McGraw-Hill, 1947 (page 84 relied on).

Mumford, W. W.: The Optimum Piston Position for Wide-Band Coaxial-to-Waveguide Transducers, Proceed- Vings of the IRE, February 1953 (pages 256-261 relied on).

HERMAN KARL SAALBACH, Primary Examiner. 

4. IN AN ARRANGEMENT FOR TUNING A WAVEGUIDE, SAID WAVEGUIDE BEING DIMENSIONED TO SUPPORT ONLY ONE MODE OF POPAGATION OVER A FREQUENCY RANGE INCLUDING A FIRST AND SECOND FREQUENCY, MEANS FOR GENERATING SAID FIRST AND SECOND FREQUENCY, MEANS FOR LAUNCHING SAID FIRST AND SECOND FREQUENCY IN SAID MODE IN THE WAVEGUIDE, FIRST ADJUSTABLE TUNING MEANS POSITIONED IN SAID WAVEGUIDE FOR PROVIDING AN IMPEDANCE MATCH AT SAID FIRST FREQUENCY, AND SECOND ADJUSTABLE TUNING MEANS POSITIONED IN SAID WAVEGUIDE FOR MAINTAINING THE SECOND TUNING MEANS REFLECTIONLESS AT SAID FIRST FREQUENCY AND FOR PROVIDING AND IMPEDANCE MATCH AT SAID SECOND FREQUENCY. 